The subject matter described herein relates to printing blankets having non-extensible backing plies such as, but not limited to metal, and more particularly to such blankets having a construction adapted to be mountable onto blanket cylinders using conventional single reel rod lockup mechanisms.
One of the most common commercial printing processes is offset lithography. In this printing process, ink is offset from a printing plate to a rubber-surfaced printing blanket mounted on a blanket cylinder before being transferred to a substrate, such as paper. Typically, the blanket cylinder comprises a chrome nickel-plated or stainless steel cylinder having a longitudinal opening or “gap” therein. An encircling rubber printing blanket is releasably mounted onto the cylinder with opposing ends of the blanket being fed into the cylinder gap and secured by a locking mechanism within the gap. The printing blanket is typically reinforced with a number of fabric and/or rubber plies along with either a fabric, metal, or other non-extensible backing. The use of a metal backing is often preferable as it prevents stretching of the blanket when it is mounted on the blanket cylinder. The metal backing also provides dimensional stability to the blanket, resulting in high print quality, eliminates the need for frequent re-tensioning of the blanket as would be required with conventional fabric-backed blankets and improves printing to the edge of the blanket cylinder gap.
There are currently a number of different types of lockup mechanisms used in the printing industry to secure printing blankets into the cylinder gap. In most conventional presses, blanket bars are typically secured to each end of the blanket and the ends are inserted into the blanket cylinder gap and secured with a lockup device.
In recent years, manufacturers of offset printing presses have equipped newer presses with a “plate” type lockup mechanism which allows the use of metal-backed or non-tensioned blankets and which achieves a very narrow printing gap. The use of the newer presses in combination with a metal-backed blanket provide faster printing speed, reduced press vibrations, higher quality print, longer blanket life, and reduced non-print length compared to standard tensioned blankets which are used with conventional bar lockup devices.
However, blankets containing a metal backing are difficult to mount and tension properly on a blanket cylinder which uses more conventional mounting mechanisms such as single or dual reel rods or “t-bar” type lockups. This is due to the metal at the leading and trailing ends of the blanket which is relatively inflexible as compared to conventional fabric-backed blankets and is difficult to feed into the cylinder gap. In addition, the stiffness of the metal-backed blankets makes it difficult to mount the blankets around small diameter printing cylinders, and the bending required to insert the blanket ends into lock up mechanisms may cause rupturing of the metal layer from the other layers in the blanket. Further, the ends of metalback blankets have a tendency to pull out or release from many locking mechanisms during high speed printing operations.
Andrew et al., U.S. Pat. No. 6,530,321 describes various embodiments of printing blankets having non-extensible (metal or polymer) backings. The blankets include reinforcing fabric layers in which the weft and warp fibers of the fabric plies are oriented such that the blankets have greater flexibility to enable easier lock-up. The blankets include different end treatments to be able to be mounted in different locking mechanisms. In one embodiment, the blanket ends include blanket bars thereon to enable lock-up in a single reel rod mechanism. However, the relatively inflexible metal base at the leading and trailing ends of the blanket makes it difficult for an operator to feed the ends into the gap in the cylinder for lockup. Additionally, the stiffness of metalback blankets makes them more difficult to mount around smaller diameter blanket cylinders.
Czerner, US Pub. No. 2007/0101884, describes embodiments of printing blankets having non-extensible polymer base layers to address the mounting difficulties encountered using relatively inflexible metalback blankets. Relief areas are provided at adjacent and opposite ends of the blankets so that the other blanket layers are not subjected to tensioning forces which may cause a gauge reduction in the blanket at the blanket cylinder gap.
Accordingly, there is still a need in the art for a printing blanket having a non-extensible backing ply such as a metalback, or other non-extensible backed, blanket which has a construction which may be easily and securely mounted into the gap of a blanket cylinder that uses a conventional single reel rod lock-up mechanism.